Blackberries are among the lowest-calorie fruits you can garnish with, but when you're slicing them for tarts, yogurt bowls, or fruit platters, the math gets fiddly fast. A single blackberry weighs only 5–9 grams and delivers just 2–4 calories, which means one thin slice can be well under a single calorie. This Blackberry Calories Per Slice Calculator works out the exact calorie value of each slice from your berry count, your slicing style, and the average berry size you're working with.
The tool is built for calorie counters, meal preppers, and anyone who logs food by the piece instead of by the gram. It uses the standard USDA reference of 43 kcal per 100 g of raw blackberries, and you can adjust that value if you are tracking a specific product label.
Enter your berry count, choose a slice style, and hit Calculate to see the per-slice, per-berry, and per-batch breakdown instantly.
⚙️ Your Blackberry Setup
Count whole berries before slicing.
USDA reference value for raw blackberries is 43 kcal per 100 g.
📊 Results
Step-by-Step Guide
Using the calculator takes less than a minute. First, enter the total number of whole blackberries you plan to slice — whether that is four berries for a dessert garnish or forty for a fruit salad topping. Next, choose how many slices you cut from each berry: 2 slices if you are halving them, 3 slices for a standard cut, or 4 thin rounds for an even lighter garnish. Then pick a berry size preset or type a custom average weight. The presets reflect typical wild and cultivated blackberry sizes: small berries around 5 g, medium around 7 g, and large ones around 9 g.
Finally, check the calorie density field. The default of 43 kcal per 100 g matches the USDA reference value for raw blackberries, so most users can leave it alone. If you are working from a packaged product label — frozen blackberries without added sugar, for example — adjust the number to match, then click Calculate. The result panel shows the calories in a single slice, the total calories for the whole batch, the calories per whole berry, and the math behind each step. Use the Reset button to restore the defaults at any time.
How the Calculation Works
The calculator uses a simple three-step proportion. First it finds the total weight of all berries by multiplying the berry count by the average weight per berry. Then it converts that weight into calories using the energy density you entered: calories = weight in grams × (calories per 100 g ÷ 100). Finally it divides the total calories by the total number of slices — berries × slices per berry — to get the per-slice value.
Formula recap:
Total weight = number of berries × weight per berry
Total calories = total weight × (calories per 100 g ÷ 100)
Calories per slice = total calories ÷ (number of berries × slices per berry)
Because blackberries are roughly 88% water, their energy density is very low. The reference figures come from the USDA FoodData Central database, which lists raw blackberries at 43 kcal per 100 g, with 9.6 g of carbohydrate, 5.3 g of fiber, and just 0.49 g of fat per 100 g. You can browse the full nutrient profile at USDA FoodData Central.
Worked Examples
Example 1 — Dessert garnish: You slice 10 medium blackberries into 3 slices each. Berry size = 7 g, so total weight = 10 × 7 = 70 g. Total calories = 70 × (43 ÷ 100) = 30.1 kcal. Total slices = 10 × 3 = 30. Calories per slice = 30.1 ÷ 30 = 1.00 kcal. Each little slice is about one calorie.
Example 2 — Large berries, halved: You halve 6 large blackberries at 9 g each. Total weight = 6 × 9 = 54 g. Total calories = 54 × 0.43 = 23.2 kcal. Total halves = 12. Calories per half = 23.2 ÷ 12 = 1.94 kcal.
Slicing & Portioning Tips
Blackberries are delicate, so a sharp paring knife gives cleaner slices than a serrated blade, which tends to crush the drupelets. If you are slicing a large batch, chill the berries first — cold fruit holds its shape much better. Because sliced blackberries release juice quickly, slice them right before serving or freezing. Slices work beautifully in yogurt parfaits, overnight oats, pancake batter, and chia puddings, and the per-slice calorie count makes it easy to log garnishes precisely.
Pro tip: For baking, weight is more reliable than berry count. If a recipe calls for 1 cup of blackberries, that is roughly 150 g — about 21 medium berries and roughly 65 kcal total. Weighing the fruit before slicing always gives the most accurate calorie log.
Reference: Blackberry Nutrition at a Glance
These values are for 100 g of raw blackberries, based on USDA FoodData Central data:
| Nutrient | Amount per 100 g |
|---|---|
| Energy | 43 kcal |
| Water | 88.2 g |
| Carbohydrate | 9.6 g |
| Dietary fiber | 5.3 g |
| Total sugars | 4.9 g |
| Protein | 1.4 g |
| Total fat | 0.49 g |
| Potassium | 162 mg |
| Vitamin C | 21 mg |
Fiber makes up more than half of the carbohydrate in blackberries, which is why their net carb count is famously low — about 4.3 g per 100 g. If you are also tracking micronutrients, see our Blackberry Iron Calculator.
Frequently Asked Questions
How much does one blackberry weigh?
It depends on the cultivar and growing conditions. Wild blackberries are often 3–5 g, while cultivated varieties such as Marion or Chester range from 5 to 9 g. When accuracy matters, weigh a small handful and divide by the berry count to get your own average.
Is calories per slice a practical way to track intake?
For garnishes and small toppings, yes. Kitchen scales rarely read accurately below a few grams, so counting slices is often more consistent than weighing one berry. The trade-off is that slices vary slightly in size, so treat the result as a solid estimate rather than a lab measurement.
Do frozen or cooked blackberries have different calories?
Frozen blackberries without added sugar have essentially the same calorie density as fresh, although freezing changes the texture. Cooking plain berries removes some water, which makes each gram slightly more calorie-dense; adding sugar to a compote, of course, raises the calorie count dramatically.
Can I use this calculator for meal prep?
Absolutely. It is handy for portioning fruit platters, topping Greek yogurt bowls, or adding blackberry slices to overnight oats. If you are tracking with an app, check whether it logs berries by cup or by gram so your numbers line up.